The NIEHS knock out core (KOC) is a servicing core facility with some research opportunity. Each project in the core is a long-term commitment from start to finish, and several projects are at different stages of completion in the core at any given time of the year. The core works very closely with the investigator since the inception of the project, which typically starts with meeting the PI's group for developing the targeting strategy and continues until the mutant mouse is made. KOC helps investigators to generate the mutant mouse customized to their research needs; including traditional knockouts, conditional knockout and knock-ins. It also provides assistance to establish and culturing the mutant cells for in vitro studies, along with dissecting the early stage embryos and help establishing the genotyping strategies.